The present invention generally relates to fluid dispensing systems, and more specifically, but not exclusively, concerns a dispensing pump that minimizes leakage and increases of the amount of fluid that can be dispensed from a container.
Fluid dispensing pumps are used in a wide variety of situations. For example, in one common situation, the fluid dispensing pump can be a manually operated pump that is used to dispense liquid hand soap in restrooms. In the case of a fixed (i.e., wall mounted) dispensing pump, aesthetics and security come into play. Typically, the pump in a fixed installation is not readily accessible except by authorized personnel such that the fluid container and associated pumping mechanism are enclosed within a cabinet or docking station. The cabinet usually has some sort of manual actuator device, such as a button or lever that can be used to manually actuate the pump and dispense the fluid. Once the fluid container is emptied, the container can be replaced with a refill unit.
One typical pump design includes a fluid intake valve that controls the fluid flow from the container into the pump, a pumping mechanism such as a piston, and a dispensing port from which the fluid is dispensed. With fluid dispensing pumps, leakage is always a concern. The mess created by the leakage is at least unsightly, and more importantly, the leakage can create hazardous conditions. For example, leakage of liquid soap from a soap dispenser onto a floor can make the floor very slippery. Moreover, fluid leakage is always a concern throughout the life of the pump. When shipping the pump, internal container pressures can fluctuate as a result of temperature changes and/or handling shocks. In the first case, a temperature increase may cause the fluid in the container to expand or gases may out gas from the fluid, thereby increasing the pressure in a fixed volume container. At some point, the pressure inside the container can increase to a great enough level so as to unseat the fluid intake valve in the pump, thereby allowing the fluid to flow into the pump. If allowed to continue, the increased pressure in the pump will cause fluid to leak out the dispensing port of the pump. Once the fluid leaks out the dispensing port, the fluid can collect inside a shipping cap for the pump, if so equipped, and soil the external surfaces of the pump. In the second case, a hydraulic pressure pulse can be mechanically created inside the container by rough or even routine handling. For instance, the hydraulic pressure pulses can be created through container vibration, the container being dropped, and/or through container impact. The hydraulic pressure pulses created through handling can have much of the same affect upon the pump as with temperature changes described above, thereby causing leakage.
Leakage of fluid from the pump can occur through other sources as well. As an illustration, one leakage source in a typical fluid pump comes from fluid remaining within the dispensing port after routine use. As one should appreciate from using hand soap dispensers, the liquid soap remaining in the dispensing port tends to drip and pool on the countertop or the floor. Many factors affect this type of leakage, such as viscosity of the fluid, surface tension, diameter of the dispensing port, and height of the fluid in the dispensing port. Any product residing within the dispensing port will have a certain associated weight. The weight of the fluid in the dispensing port imparts a force, known as head pressure, against the surface tension of the fluid that bridges the opening of the dispensing port. As should be appreciated, the greater the height of the fluid in the dispensing port, the greater weight of the fluid that bears against the surface tension of the fluid at the dispensing port. The greater weight of the fluid in the dispensing port gradually overcomes the surface tension at the opening of the dispensing port. The surface of the fluid at the opening will stretch and bulge beyond the opening of the dispensing port, thereby forming a droplet. At some point the droplet will break free as a result of an external vibration and/or the inability of the fluid to withstand the higher head pressure imparted by the greater weight.
Another leakage source can be caused by the dispensing of fluid. As fluid is dispensed from the container, a vacuum can form inside the container. Left unaddressed, the vacuum inside the container can distort the container, which in turn can cause cracks in the container and subsequent leakage from the cracks. Conceivably, even if no leakage occurs, the vacuum inside the container can become great enough to overcome the ability of the pump to dispense fluid or at the least reduce dispensing dosages.
Another factor in dispensing pump design is the need to have the pump evacuate as much of the contents in the container as possible so as to minimize waste. Typically, in order to minimize the overall container height for shipping purposes, a significant portion of the pump is placed inside the container. For inverted type pumps as well as other type pumps, this arrangement limits the amount of fluid that can be evacuated from the container since the fluid can only be drawn down to the level of the intake valve, which is positioned well inside the container. As a result, the fluid remaining in the container below the inlet valve is wasted.
To reduce vacuum formation inside the container, a number of venting structures have been developed for venting air into the container. However, these structures typically have a number of drawbacks. For example, some systems require that a valve for controlling the inflow of air be positioned inside the container, which makes the pump bulky and difficult to install. With high viscosity fluids, or even low viscosity fluids, air can become trapped in the fluid in the form of bubbles. If not properly addressed, the bubbles of air can enter the pumping chamber, thereby resulting in a short or inconsistent dose of fluid being pumped. Due to this dosing inconsistency, sometimes the pump has to be pumped repeatedly in order to deliver a sufficient amount of fluid, which can become quite frustrating to the user.
Thus, needs remain for further contributions in this area of technology.